For those who asked:

I just heard from the vet. Jack's owners finally called them back... they are from the Equine Center not too far from here, and they did get Jack as a barn cat. But they didn't realize he was declawed when they got him (hmm, don't think he really is but I'm not going to say a word about that) and so he's not a very good barn cat (ha! he's been catching all our moles), so if we want to keep him they're all right with that (damn straight).

I have the owner's name and number and will be calling her to have a chat. Right now this gorgeous, people-loving INDOOR cat is sleeping happily shedding his grey fur all over my light-colored sofa and it doesn't bother me in the least. I am not going to give him back so he can be left outdoors to get riddled with fleas and tapeworms again.

So there.

sff_corgi, you'll appreciate this: MINE.